That's some interesting math and some interesting assumptions behind the math.

I think you did a pretty good job working out the practical logistics of the ISV supply/return chain that connects Earth and Pandora.

Basically, what you're saying is you figured out that at any one time, there should be one ISV around Earth, one around Pandora, five coming from Earth to Pandora, and five returning to Earth from Pandora.

That sounds about right, all of which means that about a year after the events at the end of the movie, Jake and the Na'vi should expect to see an ISV showing up in the sky of Pandora.

Now, the only real question is what do they do at that point?

We'll find out, I am sure.

(however, I think the last "routine" ship to leave Earth would still be able to stop and turn around if they got enough advance warning that the situation has changed on Pandora)